<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      if (true) {
        // 仅在当前块级作用域中有效
        let a = 100
        console.log(a) // 100
      }

      for (let i = 0; i < 3; i++) {
        console.log(i)
      }
      //   console.log(i); //  报错
    </script>
  </body>
</html>
